Conventionally, aluminum (Al) alloy films have been used in the wiring of the display devices represented by liquid crystal displays. However, with the growth in size and the high definition of the display devices, problems resulting from a fact that a wiring resistance is large, such as signal delay and electrical power loss, are coming to the surface. Accordingly, copper (Cu) having a resistance lower than that of Al attracts attention as a wiring material. The electrical resistivity of Cu is as low as 1.6×10−6 Ω*cm, whereas that of Al is 2.5×10−6 Ω*cm.
However, Cu has the problem that the adhesiveness thereof to a glass substrate is low, and may be peeled off. In particular, in the case of a soda-lime glass substrate (glass substrate comprising silicic acid, soda ash, and lime as the main materials) that is inexpensive and capable of being processed to have a large area, peel off of a wiring material, occurring due to the migration of alkali metal elements contained in the glass substrate, such as Na, becomes a problem. Also, there is the problem that, because the adhesiveness of Cu to a glass substrate is low, it is difficult to perform wet etching for processing Cu into a wiring shape. Therefore, various techniques for enhancing the adhesiveness between Cu and a glass substrate are proposed.
For example, Patent Documents 1 to 3 disclose techniques in each of which the adhesiveness is intended to be enhanced by interposing a layer composed of a metal having high melting temperature, such as molybdenum (Mo) or chromium (Cr), between Cu wiring and a glass substrate. In these techniques, however, a process for forming the layer composed of a metal having high meting temperature becomes further necessary, and accordingly the manufacturing cost of a display device is increased. In addition, because dissimilar metals of Cu and a metal (Mo, or the like) having high melting temperature are laminated one on another, there is the fear that corrosion may occur on the interface between Cu and the metal having high melting temperature when wet etching is performed. Further, because there is a difference in the etching rate between the dissimilar metals, the problem that the wiring section cannot be formed into a desired shape (e.g., a shape having a taper angle of approximately 45 to 60°) may arise. Furthermore, because the electrical resistivity of a metal having high melting temperature, for example, that of Cr (12.9×10−6 Ω*cm), is higher than that of Cu, and accordingly a signal delay or electrical power loss, occurring due to the wiring resistance, becomes a problem.
Patent Document 4 discloses a technique in which nickel or a nickel alloy, and a polymer resin film are interposed as an adhesive layer between Cu wiring and a glass substrate. In the technique, however, the resin film is deteriorated in the high-temperature annealing process during the manufacture of a display device (e.g., liquid crystal panel), and accordingly there is the fear that the adhesiveness thereof may be decreased.
Patent Document 5 discloses a technique in which copper nitride is interposed as an adhesive layer between Cu wiring and a glass substrate. However, copper nitride itself is not a stable compound. Accordingly, in the technique, N atoms are released as N2 gas in the high-temperature annealing process during the manufacture of a display device (e.g., liquid crystal panel), resulting in the deterioration of the wiring film, and accordingly there is the fear that the adhesiveness thereof may be decreased.